OBJECTIVE—Genital tract infection accounts for ~ 25–40% of all pre-term births. We sought to
assess the relationship between preterm birth and selected vaginal bacterial taxa associated with
preterm birth either directly or through their association with bacterial vaginosis (BV).
STUDY DESIGN—Vaginal fluid for Gram stain was collected between 17 and 22 weeks
gestation as part of a randomized trial of ultrasound-indicated cerclage for preterm birth
prevention in women at high risk for recurrent spontaneous preterm birth. Bacterial DNA was
extracted from the Gram stain slides and analyzed using quantitative PCR.
RESULTS—Among the 499 participants, Mycoplasma was positively correlated with increased
risk of preterm (RR = 1.83; 95% CI: 1.52,2.22) as was Mobiluncus (RR=1.36; 95% CI: 1.07, 1.73)
and Atopobium (RR=1.44; 95% CI: 1.1, 1.87). However, there were strong interactions between
race/ethnic group and the presence of these and other individual taxa on risk of preterm birth. By
contrast, BVAB3 was consistently associated with a reduction in risk of preterm birth for all
racial/ethnic groups (0.55; 95%CI: 0.39, 0.78).
CONCLUSIONS—BV is characterized by a reduction of Lactobacillus, and lactic acid
producing bacteria and the presence of Mobiluncus; we found these factors and presence of
Mycoplasma to be associated with increased risk of preterm birth. By contrast, the presence of a
recently identified organism sufficient to cause BV, BVAB3, decreased risk of preterm birth.
These findings give insight into why treating BV has mixed impact on risk of preterm birth.

We examined the community ecology of vaginal microbial samples taken from pregnant women with previous preterm birth experience to investigate whether targeted pathogenic and commensal bacteria are related to risk of preterm birth in the current pregnancy. We found a significant correlation between the community structure of selected bacteria and birth outcome, but the correlation differed among self-reported racial/ethnic groups. Using a community ordination analysis, we observed infrequent co-occurrence of Mycoplasma and bacteria vaginosis associated bacteria 3 (BVAB3) among black and Hispanic participants. In addition, we found that the vaginal bacteria responded differently in different racial/ethnic groups to modifications of maternal behavioral (ie, douching and smoking) and biological traits (ie, body mass index [BMI]). Even after accounting for these maternal behaviors and traits, the selected vaginal bacteria was significantly associated with preterm birth among black and Hispanic participants. By contrast, white participants did not exhibit significant correlation between microbial community and birth outcome. Findings from this study affirm the necessity of considering women’s race/ethnicity when evaluating the correlation between vaginal bacteria and preterm birth. The study also illustrates the importance of studying the vaginal microbiota from an ecological perspective, and demonstrates the power of ecological community analysis to improve understanding of infectious disease.